audiopolicy: Check if A2DP playback happens via primary output

Audio policy implementation assumes A2DP playback to happen
via HW module other than the primary HAL.This need not be true
always, since primary audio HAL can support A2DP playback too.

Add an api to check if A2DP playback is supported via primary HAL,
and if it is supported avoid suspendOutput.

Change-Id: I13bf8137ab64e257d84791dd77ee746dec39dec4